A current trend in supermarket check-out stand technology is the incorporation of a scale into the check-out counter surface. Typically, these scales overlay check-out scanning devices, the scale having an aperture therein which permits the checker to use the limited space of a check-out counter for both scanning product bar code labels as well as weighing produce. An example of this type of scale is manufactured by Shekel Electronics, Inc., and designated as Model SC 150. A marked advantage of such a scale is the elimination of a separate scale at some distance from the check-out counter which decreases the ability of the checker to quickly check through customers waiting in line.
Although this type of scale is becoming increasingly popular, it does exhibit a fault in terms of precision. This arises due to the fact that large produce or goods to be weighed often extend beyond the periphery of the scale and come to rest on the check-out counter surface. This results in a lower weight being recorded than is actually the case. Accordingly, the supermarket undercharges its customer. A second precision problem is due to having products from either side of the belt or bagging area touch the scale surface thus creating an incorrect weight and overcharging the customer.
It would, therefore, be desirable to detect situations where inaccurate weighing is taking place due to poor positioning of produce or other goods on a check-out counter scale, or other types of interference with the scale weighing plate.